1. Field of the Invention
The present invention relates to an air bag device which blows gas from an inflator into a folded air bag so as to inflate to unfold the air bag, and also to a method for accommodating the air bag in the air bag device.
2. Description of the Related Art
Recently in a vehicle, an air bag device is used which is mounted in a portion fixed to a vehicle body, for example, a steering wheel in an interior of the vehicle and which inflates to unfold an air bag due to a large acceleration being applied to the vehicle.
As the above-described air bag device, there is known, for example, the structure illustrated in FIGS. 19 to 21. In the air bag device 10 shown in these figures, an inflator 14 which is a gas generator is disposed at the center of a retainer 12 which is a supporting plate, and an air bag 18 is disposed to enclose gas ejecting holes 16 of the inflator 14 and is also covered with a module cover 20. In order that the air bag 18 thus disposed be provided in a narrow space formed between the inflator 14 and the module cover 20, the air bag 18 is accommodated compactly in a folded state.
Conventionally, as a method of folding the air bag 18, there is known a folding method which is called a so-called roll winding method. In this roll winding method, the air bag 18 of a circular flat surface in a developed state is, first, wound into a roll from both ends thereof in the diametrical direction to a front surface which faces a vehicle occupant in a state in which the air bag 18 inflates to unfold and where an aperture 18A into which the inflator 14 is inserted is not formed, so as to be folded up to become elongate (rectangular), thereby forming a first folding portion 24.
Next, the air bag 18 folded substantially into a rectangle is wound into a roll from both ends thereof to a rear surface, which is opposite to the front surface, with the aperture 18A formed thereon and a pair of roll portions 22 are thereby formed as post-folding portions.
The pair of roll portions 22 are each wound to the position near the aperture 18A and folded toward the front surface with no aperture 18A formed and in a direction opposite to the direction in which each roll portion 22 is wound, to form reversed portions 23. As a result, the folding method of roll winding type as shown in FIG. 19 is completed. In the roll winding system, the pair of roll portions 22 which are the post-folding portions are disposed adjacently so as to contact each other, and the first folding portion 24 which is a portion of the air bag 18 and folded preceding the pair of roll portions 22 is positioned between the pair of roll portions 22 and the inflator 14.
As shown in FIG. 19, in the air bag device in which the air bag 18 is accommodated in a state of being wound into rolls, when an acceleration sensor (not shown) detects a large acceleration of a predetermined value or more applied to the vehicle, the inflator 14 is actuated to generate gas. The gas generated in the inflator 14 blows out from the gas ejecting holes 16 to push to expand the first folding portion 24. As a result, as illustrated in FIG. 20, the pair of roll portions 22 are pushed by the expanded first folding portion 24 to break the module cover 20 along a groove-shaped break portion 26, and therefore, the pair of roll portions 22 are pushed out. Moreover, when the first folding portion 24 continues to expand by gas continuously ejected from the gas ejecting holes 16 of the inflator 14, the pair of roll portions 22 located at the front side in the direction in which the first folding portion 24 expands (i.e., the direction indicated by arrow A in FIG. 20) are pushed out by the first folding portion 24, and as a result, the pair of roll portions 22 moves rapidly toward the front side of the air bag device 10, i.e., in the direction indicated by arrow A and is thereby unfolded. Subsequent to this operation, when the air bag 18 is filled with gas ejected from the inflator 14, the air bag 18 inflates to unfold in the direction indicated by arrow B in FIG. 21 so as to be brought into a final expanding state having a slightly compressed spherical configuration.
Thereafter, the air bag 18 gradually becomes deflated in such a manner that gas is let out from an air hole.
In the above-described folding system in which the air bag 18 is wound into a roll, during an expanding operation of the air bag 18, the roll portions 22 which are the post-folding portions move toward the front side indicated by arrow A preceding the first folding portion 24 so as to expand toward the front side of the air bag device, and thereafter, as gas is fed from the first folding portion 24 of the air bag 18 to the roll portions 22, the roll portions 22 are each pulled back in a direction opposite to that indicated by arrow A (i.e., toward the rear side of the air bag device 10), and simultaneously, inflate to unfold in the directions indicated by arrows B (i.e., the left-and-right directions of the air bag device 10). As a result, the air bag is subjected to the expanding process so as to be brought into a final expanding state to have a compressed spherical configuration. For this reason, it is not possible that the entire air bag 18 expands uniformly through the expanding process in such a manner as to enlarge a ring of a concentric circle from the central portion thereof.